For tracking an area including a specific target through captured images (hereinafter, image frames) input from an imaging unit in time series, in the prior art, a target area 50 is decided from a first image frame F0 and tracked through subsequent image frames F1 to Fn as shown in FIG. 6.
FIGS. 7A to 7C show an example of results of the tracking process. From the target area 50 on the image frame F0 in FIG. 7A, a new target area 51 on the image frame F1 in FIG. 7B is acquired. Then, a new target area 52 on the image frame F2 in FIG. 7C is acquired from the target area 51. Thereafter, the same process is repeated.
There is a problem that an error in a result of tracking occurs due to a movement, deformation or change of posture of a target and is accumulated as the target area is updated. FIG. 7C shows an example of a tracking failure that the target area 52 is largely shifted from the original target area 53 of the first image frame F0. Moreover, the tracking error may cause an increase in the size of the target area, resulting in an increase in amount of calculation in the tracking process and delaying the processing speed.
Japanese Patent Application Publication No. 2008-153879 discloses an imaging device which tracks a target on an image frame of a captured image and adjusts a torque amount of an imaging unit using a motion vector as a result of the tracking, for example. However, this device still cannot eliminate a tracking error affecting a tracking result.
For another example, Japanese Patent Application Publication No. 2009-10453 discloses a technique to correct a tracking result without intermitting the tracking by allowing a user to input a desired target point on the tracking result.
However, a problem arises in this technique that since a target area is searched while expanding or shrinking the tracking result, an amount of calculation for the tracking process becomes enormous, extremely delaying the processing speed.